Method for pretreating biomass to produce bioethanol

Abstract

Disclosed is a method for preparing bioethanol from biomass. The feedstock for preparation of bioethanol, i.e. the biomass, is pretreated by a combination of chemical and physical methods. The method is advantageous in that detoxification is unnecessary since the substances that inhibit fermentation are not produced and acid reconcentration for recycling is not needed. Further, since the sonication makes saccharification easier, removal of lignin (delignification), which interferes with the saccharification of cellulose, is unnecessary. Accordingly, the present disclosure allows to produce bioethanol with high yield and at low cost in an environment-friendly manner.

1. A method for preparing ethanol from biomass, comprising the steps of:
 (a) pulverizing biomass; 
 (b) hydrolyzing the pulverized biomass by treating with sulfuric acid; 
 (c) separating the resultant of the step (b) into liquid and solid phases; 
 (d) (d-1) neutralizing the liquid phase of the resultant of the step (c) by treating with calcium carbonate (CaCO 3 ) as a neutralizer to obtain pentose and to form CaSO 4 , and, (d-2) sonicating the solid phase of the resultant of the step (c) and treating the same with cellulase to obtain hexose; and 
 (e) fermenting the pentose and hexose of the step (d-1) and (d-2) by treating with ethanol-producing fermenting microorganism. 
 
     
     
       2. The method according to  claim 1 , wherein the biomass is selected from a group consisting of rice straw, wheat straw, corn cob, corn stover, rice husk, paper, wood, sawdust, agricultural waste, grass, sugar cane bagasse, cotton, flax, bamboo, abaca, algae, fruit skin and seaweed. 
     
     
       3. The method according to  claim 1 , which further comprises, between the step (a) and the step (b), a step of (a-1) passing biomass pulverized in the step (a) through meshes with one side being 0.25-5 mm in length. 
     
     
       4. The method according to  claim 1 , wherein the hydrolysis in the step (b) is performed with a 0.1-10% (v/v) acid at 100-150° C. for 20-60 minutes. 
     
     
       5. The method according to  claim 1 , wherein the sonication in the step (d-2) is performed by applying sonic waves of 15-130 kHz for 0.5-36 hours to the acid hydrolyzed solid phase in the step (c). 
     
     
       6. The method according to  claim 1 , which further comprises French pressing after the sonication in the step (d-2). 
     
     
       7. The method according to  claim 6 , wherein the French pressing is performed at 25,000-40,000 psi. 
     
     
       8. The method according to  claim 1 , wherein the cellulase treatment in the step (d-2) is performed at pH 4-7 and 30-70° C. for 24-48 hours. 
     
     
       9. The method according to  claim 1 , wherein the ethanol-producing fermenting microorganism in the step (e) is yeast. 
     
     
       10. The method according to  claim 9 , wherein the yeast belongs to the genus  Saccharomyces, Schizosaccharomyces, Sporobolomyces, Torulopsis, Trichosporon, Wickerhamia, Ashbya, Blastomyces, Candida, Citeromyces, Crebrothecium, Cryptococcus, Debaryomyces, Endomycopsis, Geotrichum, Hansenula, Kloeckera, Lipomyces, Pichia, Rhodosporidium  or  Rhodotorula.    
     
     
       11. The method according to  claim 10 , wherein the yeast belonging to the genus  Saccharomyces  is  Saccharomyces cerevisiae, Saccharomyces baynus  or  Saccharomyces carlsbergensis.    
     
     
       12. The method according to  claim 1 , wherein the step (d-2) further comprises a step of pulverizing the solid phase before the sonication of the solid phase. 
     
     
       13. The method according to  claim 12 , wherein the pulverized solid phase has an average particle diameter from 0.1 mm to 2 cm.